1. Field
The presently disclosed subject matter relates to LED (light emitting devices) devices and LED lighting apparatuses, and more particularly to the LED devices that can emit a plurality of substantially natural color lights, and to the LED lighting apparatus using the LED devices that can selectively emit a light mixture with a preferable color tone by using the plurality of natural color lights.
2. Description of the Related Art
Recently, LED devices have been widely used as a light source for general lighting, a back light unit for an LCD (liquid crystal display), a vehicle lamp, etc. One reason for such wide use is that LED devices can emit various color lights including white color light. LED lighting apparatuses that can selectively change a light-emitting color have also been commercialized in order to meet customer needs for matching the light-emitting color to interior decor and atmosphere of a room, as well as to match the light-emitting color of the back light unit to the optical characteristics of various LCD devices, etc.
This is due to customer needs for general lighting that includes a wide range of white light from a white light, of cool color such as a natural light in daytime, to a warm color such as a light of bulb. In addition, white LED devices are basically composed of an LED chip having a peak wavelength towards a short wavelength in the visible light range or an LED chip having a peak wavelength in an ultraviolet light range and an encapsulating resin including a phosphor so that the white LED devices can emit white light by exciting the phosphor with light emitted from the LED chip.
Therefore, white LED devices using phosphor can be subject to various variations in optical characteristics such as color tone (spectrum distribution), brightness, chromaticity, and the like, because of variability in the density of the phosphor in the encapsulating resin, variability of thickness of the encapsulating resin, variability of the spectrum distribution of the LED chip, etc. The optical variations of the white LED devices may also cause various variations in the optical characteristics of LED lighting apparatuses using white LED devices.
Consequently, in general lighting using LED lighting apparatuses, in the back light unit using white LED devices and in other lighting units using white LED devices, these various optical variations may reduce the commercial value of the LED lighting apparatuses. When these white LED devices and LED lighting apparatuses are produced, products that can conform to each specification of general lighting, the back light units and the like can be selected in their manufacturing processes. However, the method may result in increased product cost. To that end, various LED lighting units using white LED devices that can reduce optical variations have been developed.
For example, an LED lighting unit and a LCD apparatus using the same is disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP2001-209049). FIG. 8 is a circuit diagram showing a conventional LED lighting unit including an adjustable function for chromaticity, which is disclosed in Patent Document No. 1. The conventional LED light unit includes a plurality of light sources 53.
Referring to FIG. 8, the one light source 53 includes: a white LED 51 made by encapsulating a blue LED chip 50 with an encapsulating resin including a phosphor; an LED chip 52 located adjacent the white LED 51 so that the LED chip 52 (e.g. a yellow LED) can adjust the chromaticity of light emitted from the light source 53 that is based upon the white LED 51; a resistor (r) being electrically connected to the white LED 51 in series in order to determine an LED current of the white LED 51; and a variable resistor (R) being electrically connected to the LED chip 52 in series in order to be able to adjust the chromaticity of the light emitted from the light source 53.
The serial circuit of the white LED 51 and the resistor (r) is connected between a power supply and a ground in parallel along with the serial circuit of the LED chip 52 and the variable resistor (R) for adjusting the chromaticity. In addition, the plurality of light sources 53 is connected between the power supply and the ground in parallel with respect to each other. When the chromaticity of the light source 53 is adjusted, a light intensity of the LED chip 52 is adjusted by changing a current of the LED chip 52 with the variable resistor (R). Therefore, the chromaticity of a light mixture emitted from the plurality of light sources 53 may be adjusted to a favorable chromaticity by adjusting each of the variable resistors R of the light sources 53 while measuring each chromaticity of the plurality of light sources 53.
However, the above-described light sources 53 maintain the white LEDs 51 at a substantially constant light intensity, and the chromaticity of a light mixture of white light emitted from the white LEDs 51 and single color lights emitted from the LED chips 52 may be controlled by adjusting each of the light intensities of the single color lights (e.g. yellow light). In this case, the light intensity of the single color light is controlled by adjusting the current to the LED chip 52. However, the adjustable sensitivity of the light intensity with respect to the current of an LED chip emitting a single color light may be high. Thus, it may be difficult to tweak or adjust the chromaticity of the light mixture of the white lights emitted from the light sources 53.
In addition, the light source 53 includes two kinds of LED chips of which the spectrum distributions are different, and each spectrum of the light mixtures emitted from the plurality of light sources 53 can be subject to a variation with respect to a predetermined spectrum. Therefore, the control process for adjusting the chromaticity of the light mixtures emitted from the light sources 53 may become more difficult due to a complex variation of the respective variations in the light mixtures.
Moreover, when a color temperature of the light mixture emitted from the light sources 53 is located near a black body of a chromaticity coordinate in the CIE chromaticity diagram, the single color light emitted from the LED chip 52 is located far away from the black body of the chromaticity coordinate. Therefore, the color temperature of the light mixture emitted from the light sources 53 cannot be located other than at a position that is close to an intersection of the black body coordinate line and a virtual line between a chromaticity coordinate of the single color light emitted from the LED chip 52 and that of the white light emitted from the white LED 51.
Thus, when the color temperature of the light mixture emitted from the light sources 53 is located on the substantially black body of the chromaticity coordinate so that the light mixture can become a white light that is close to a natural color, the color temperature will be located in a very small area on the black body. Consequently, it may be impossible for the light sources 53 to emit light having a color temperature within a wide range of the substantially black body.
As a measure that emits light having a color temperature on the substantially black body, for example, an LED lighting unit having a variable color temperature is disclosed in Patent Document No. 2 (Japanese Patent Application Laid Open JP2005-101296). If the conventional LED lighting unit is described with reference to FIG. 8, the LED lighting unit includes a first white LED 51 and a second white LED 52, and the first and the second white LEDs 51, 52 are composed of the same blue LED chips.
However, a first encapsulating resin for the first white LED 51 is made by dispersing a yellow phosphor into an epoxy resin, and a second encapsulating resin for the second white LED 52 is made by dispersing the yellow phosphor and an orange phosphor into the epoxy resin. When the white LEDs 51 and 52 are turned on by providing them via the resistors (r) and (R) with the power supply +B, each of white lights having different color temperatures can be emitted from the first white LED 51 and the second white LED 52.
In this case, the white light that is emitted from the first white LED 51 has a color temperature, for instance, between 6000K and 7000K. The white light that is emitted from the second white LED 52 has a color temperature, for example, between 3000K and 4000K. Therefore, the conventional LED lighting unit can selectively emit a light mixture having a color temperature on an approximate line between the respective white chromaticity of these lights emitted from the first white LED 51 and the second white LED 52, which are located close to the black body in the CIE chromaticity diagram by adjusting their current values via resistors (r) and (R).
However, in the above-described conventional LED lighting unit, the phosphor that is included in the first white LED 51 and the phosphor that is included in the second white LED 52 are different. Thus, two mixing processes are required for the epoxy resins and these mixing processes, each using different phosphors are carried out under strict density management. However, it may be unavoidable for some variations to occur in the distribution densities between the epoxy resins and the different phosphors even when trying to control the respective accuracies of the different distribution densities within the ranges of two predetermined densities during the mixing processes.
Thus, in the first encapsulating resin and the second encapsulating resin, an individual variability of the distribution densities between the epoxy resin and the phosphors may occur. The individual variations of these distribution densities may cause respective variations in the optical characteristics such as brightness and wavelength distributions of the light emitted from the first white LED 51 and the second white LED 52.
Therefore, because the light mixture emitted from the LED lighting unit includes the respective light emitted from the first and the second white LEDs 51 and 52, the LED lighting unit may emit a light mixture that includes the respective variations in the optical characteristics such as the brightness and the wavelength distributions of the light emitted from the first and the second white LEDs 51, 52. Thus, it may be difficult for the LED lighting unit to reliably emit light having a favorable color temperature because the color reproducibility in the optical characteristics may be poor even if the color temperature is controlled by the current value.
To resolve the above-described issues, an LED lighting unit and method for manufacturing the same is disclosed in Patent Document No. 3 (Japanese Patent Application No. 2008-279991) by the inventor of the presently disclosed subject matter. FIG. 9 is a cross-sectional view showing the conventional LED lighting unit that is disclosed in Patent Document No. 3. The LED lighting unit 61 includes a first cavity 67 and a second cavity 68 in which the respective depths are different.
The first and the second cavities 67, 68 are formed by a casing 63, which is composed of a first board 66, a second board 65 and a third board 64. The first cavity 67 is formed by through-bores of the second board 65 and the third board 64, and the second cavity 68 is formed by a through-bore of the third board 64. Blue LED chips 62, which are substantially the same, are mounted in the first cavity 67 and the second cavity 68, and a substantially same encapsulating resin including a phosphor is disposed in the first cavity 67 and the second cavity 68.
Therefore, two white lights having different color temperatures can be emitted from the first cavity 67 and the second cavity 68, because the thicknesses of the encapsulating resin including the phosphor is different between the first and second cavities 67, 68. In addition, the variability of the optical characteristics of the white lights can be reduced by using the substantially same LED chips and the substantially same encapsulating resin, and their color temperatures can be located on the substantially black body of the chromaticity coordinate by changing each thickness of the encapsulating resin. Thus, the LED lighting unit can selectively emit light having a favorable color temperature between the color temperatures that are located on the substantially black body using the above-described two white lights.
The above-referenced Patent Documents are listed below, and are hereby incorporated (including their English translations) in their entirety.
1. Patent document No. 1: Japanese Patent Application Laid Open JP2001-209049
2. Patent document No. 2: Japanese Patent Application Laid Open JP2005-101296
3. Patent document No. 3: Japanese Patent Application No. 2008-279991
In the LED lighting unit that is disclosed in Patent document No. 3, although the optical characteristics may be excellent, two kinds of cavities having a different in depth are required to obtain the optical characteristics. Therefore, the manufacturing process may include a process that laminates the third board on the second board.
The disclosed subject matter has been devised to consider the above and other problems, features and characteristics. Thus, an embodiment of the disclosed subject matter can include the LED device that can selectively emit a mixture light having a preferable color temperature between two color temperatures that are close to natural colors using white lights having different color temperatures emitted from a cavity, which can include LED chips and an encapsulating resin including a phosphor in the cavity. In addition, the light mixture emitted from the LED device can maintain high reproducibility of its optical characteristics with stability.